Glass filaments are typically attenuated from bushing tips located at the bottom of a heated bushing containing molten glass. The filaments as they are attenuated are passed across the application surface of an applicator where a binder and/or size is applied to the filaments. Then, the filaments are passed into a gathering means, such a a gathering shoe, which is typically a grooved wheel or cylinder formed of a material such as graphite, with the filaments being gathered into one or more unified strands in the grooves of the gathering shoe. The thus formed strands are then passed to an attenuator, which attenuator provides the forces necessary to pull or attenuate the filaments from the bushing. As used herein, the term attenuator refers to an apparatus which may attenuate the filaments and advance the strand or to an apparatus for advancing a previously formed strand in its movement. This attenuator may be the rotating surface of a winder, a belt attenuator, a wheel attenuator or the like. Other strand materials, such as nylon, polyester and the like are similarly attenuated through orifices.
When strands, such as glass strands, nylon strands, polyester strands and the like, are collected to be packaged in bulk containers or laid down as a continuous strand mat, they often are not collected on a rotating surface, but are attenuated by means of a belt or wheel attenuator onto the mat surface. It is also possible to form strand mats by directing previously formed strand from forming packages onto the mat formation surface with an attenuator. In this case, the attenuator, or strand advancing apparatus, does not actually attenuate the filaments. Rather, in this case the attenuator merely acts to remove strand from the forming package and direct it onto the mat formation surface.
Wheel attenuators, such as those shown in U.S. Pat. No. 3,676,096 and U.S. Pat. No. 3,746,230, are often unsatisfactory. These attenuators, which employ only the cohesive forces of the wet strand against the wheel surface to attenuate the filaments, often supply insufficient tractive forces for attenuating the filaments, do to slippage. In addition, these attenuators are prone to strand wraps, wherein the strand does not exit the wheel at the desired point but rather loops around the wheel and begins to form a package of strand on the wheel, as is routinely done in the formation of forming packages on a rotating collet. Such slippage and strand wraps interfere with the production of the strand and/or the mat.
To overcome the inefficiencies of the wheel attenuators, belt attenuators have been produced. Typical of the belt attenuators which are known are those shown in U.S. Pat. Nos. 2,690,628; 3,293,013; 3,887,347; 3,955,952; 3,997,308; and 3,999,971.
In these attenuators, the strand material passes between a pair of belt surfaces, which surfaces are maintained tightly against one another. Attenuation thus results by the action of the two belts against the strand as the belts and strand progress along their paths. While these attenuators have improved the problems of slippage and strand wraps, they have created new problems of their own. In order for these attenuators to function properly, the belts must maintain tight contact with one another and with the strand material. If this tight contact is not maintained, slippage will again result. This tight contact and continuous motion results in abrasion of the belts and requires frequent replacement of the belts, adding to the cost of producing the product both in downtime and equipment costs.
In order to overcome the problems of the wheel attenuators and the problems of the belt attenuators, hybrid belt-wheel attenuators have been developed. These attenuators employ a single belt which is driven around a plurality of wheels. The strand is attenuated between the belt and one of the wheels. This wheel may have discontinuous surface, to both reduce contact of the strand with the wheel and thus abrasion of the wheel and the belt and to prevent strand wraps. This wheel also provides the driving force for the belt.
Problems have arisen with such hybrid attenuators. First, since the driving force for the belt is accomplished on the same surface of the belt as the tractive forces on the strand, and since this belt must be maintained extremely tight on the wheels to provide for this driving and attenuative action, the belt surface quickly deteriorates. Second, even with the taut surfaces of the belt, slippage of the strand material between the belt and the attenuation wheel has been a problem.
It is thus desirable to produce an attenuator or strand advancing apparatus which overcomes the slippage and strand wrap problems of wheel attenuators and the wear problem of belt attenuators.